Polyphenols, such as polyphenols prepared from the condensation of glyoxal and a molar excess of phenol in the presence of an acid catalyst, find utility in the same manner as other polyphenols and particularly for preparing epoxidized polyphenols which can be used for coatings and electronic applications as well as adhesives and laminates in the production of printed circuit boards.
The polyphenols of this invention will typically contain from about 1% to about 6% of the tetraphenols of ethane. When the phenol is phenol itself, the tetraphenol is tetrakis(p-hydroxyphenyl) ethane which is also referred to as TPE. Although the reaction products of the phenol-glyoxal reaction are mixtures, individual polyphenols such as TPE as well as other components thereof can be crystallized out of solution by conventional techniques. Thus, the level of tetraphenol ethanes, such as TPE in the phenol-glyoxal condensation products, can be greatly reduced to essentially zero by methods well known in the art without sacrifice of desirable optical properties provided by this invention. Illustratively, use of solvents such as alcohol-aromatic hydrocarbon mixtures and water miscible ketone-water mixtures are effective in this regard.
The compositions of this invention are particularly useful when automatic optical inspection (AOI) is used for quality control of laminates. The polyphenols of this invention alone, or in blends with phenolic novolacs, or after epoxidation of the polyphenols, are useful for AOI as are adducts with epoxy resins and adducts of epoxidized phenolic-glyoxal condensates with phenolic novolacs. The AOI is typically performed by measuring: fluorescence at wavelengths in the range of about 450 nm (nanometers) to about 650 nm, particularly at an excitation wavelength of about 442 nm; and/or ultraviolet (UV) light absorbance in the wavelengths of from about 350 to 365 nm.
Applicant has found a set of process conditions together with monomers and certain catalysts for obtaining polyphenols and epoxidized derivatives thereof having UV absorbance and/or fluorescence which is substantially higher than phenol-glyoxal condensates prepared by other methods within the wavelengths generally used for AOI quality control. Photoimageable materials are used in conjunction with these condensates. High UV absorbance is desirable for the manufacture of laminates used in electronic applications such as high density multilayer printed circuit boards.
Advantages of this invention include: (a) preparation of an essentially metal ion-free polyphenol without recourse to catalyst filtration or neutralization and water washing steps wherein recovery of phenol is simplified and the reactor yield is increased in those cases where the catalyst is not neutralized with a metal ion; (b) preparation of polyphenols as well as the epoxidized derivatives thereof which exhibit improved optical properties, e.g., high fluorescence and/or UV absorbance in the wavelengths used for AOI; and (c) preparation of polyphenols with increased solubility in organic solvents.
The prior art discloses many methods for making polyphenols and epoxidized derivatives thereof. But the prior art does not use the combination of monomers, reaction conditions, or catalyst which applicant uses for obtaining the desirable properties of the products of this invention. Also, the prior art does not disclose phenol-glyoxal condensates having the desirable optical properties of this invention.
As used herein, the following terms have the following meanings:
(a) "phenol-glyoxal condensation product" shall refer to the phenol-glyoxal reaction product produced by the method of this invention wherein such condensate contains less than 5% of unreacted phenol, preferably less than 3% of unreacted phenol and particularly less than 1.5% of unreacted phenol.
(b) "aldehyde equivalents" is a method for measuring aldehyde units and shall refer to aldehyde and any ketone units which may be formed in the reaction mixture or in the glyoxal charged or to be charged when measured by the below described method. Such measurements are generally reported in percent of aldehyde equivalents reacted in comparison with the aldehyde equivalents charged or to be charged to the reaction mixture. Thus, if measurements of aldehyde equivalents in a mixture of the glyoxal and phenol charged show X aldehyde equivalents and measurements after reaction in the reaction mixture later show aldehyde equivalents of 1/2 of X, then the aldehyde equivalents in the reaction mixture are 50% of that charged. During the reaction, some ketone groups may also be formed which are included in measuring of the aldehyde equivalents and are considered as part of the aldehyde equivalents herein.
The method for determining aldehyde equivalents is by taking 1.0 gram of reaction mixture and diluting it with 50 ml of methanol. The pH is then adjusted to 3.5 with dilute sodium hydroxide. There is then added, to the pH adjusted sample, 25 ml of 10% hydroxylamine hydrochloride with stirring. The sample is stirred for 10 minutes and then the sample is back titrated with 0.25 Normal (N) sodium hydroxide to pH of 3.5. The number of milliliters (mls) (the titre) of the sodium hydroxide solution used to back titrate the sample to a pH of 3.5 is used to calculate the aldehyde equivalents. The mls of sodium hydroxide solution in the titre is adjusted by correcting by titration with sodium hydroxide for the methanol and hydroxylamine hydrochloride reagents used in the test and this is referred to as the mls blank.
The aldehyde equivalents for the sample are then determined by the following formula: (2.9 times 0.25 N times (mls sodium hydroxide titre minus the mls of the sodium hydroxide in titrating the blank). The value obtained by this formula is then compared to the aldehyde equivalents obtained by the above method and formula based on one gram of an unheated, catalyst free mixture of phenol and glyoxal in the weight ratio of glyoxal to phenol used until that time or the time in question in order to determine the percent aldehyde equivalents reacted.
Unless otherwise indicated, the fluorescence measurements herein are as the maximum counts per second for a 0.05% solution of the material in question dissolved in tetrahydrofuran (THF) at an excitation wave length of 442 nm for an acquisition time of one second with a CM 1000 instrument when measured within the range of about 450 to 650 nm. CM 1000 refers to Cure Monitor 1000 which is an instrument made by Spectra Group Ltd., Inc. of Maumee, Ohio. Acquisition time is the exposure time at the designated wavelength. A count is a basic unit used by a large number of light measuring devices for data output and refers to a process of digitization of accumulated signal. In the case of a CCD detector that is used by Spectra Group Limited, Inc. of Maumee, Ohio and which was used for the data set forth herein, light produces an electrical charge on the detector that is subsequently read out by a digitizer. The digitizer is set to record one count for approximately every 10 units of charge (electrons) it reads.
The fluorescence measurements are on a comparative basis among the various materials such as in each of the tables set forth herein and not as absolute numbers. Thus, the fluorescence values of polyphenols within any one of the tables set forth later herein are relative to other polyphenols within the same table, but comparisons cannot be made with the same or other polyphenols in other tables.
The UV absorbance values are obtained from samples prepared by dissolving the material in question in THF (tetrahydrofuran) at a concentration of 10 mg (milligrams) per 100 ml (milliliters) and the absorbance measurement made at 350 nm or 365 nm.